Achieving ultra-high nitrogen and phosphorus removal from real municipal wastewater in a novel continuous-flow anaerobic/aerobic/anoxic process via partial nitrification, endogenous denitrification and nitrite-type denitrifying phosphorus removal.

Achieving economic and efficient removal of nutrients in mainstream wastewater treatment plants (WWTPs) continues to be a challenging research topic. In this study, a continuous-flow anaerobic/aerobic/anoxic system with sludge double recirculation (AOA-SDR), which integrated partial nitrification (PN), endogenous denitrification (ED) and nitrite-type denitrifying phosphorus removal (nDNPR), was constructed to treat real carbon-limited municipal wastewater. The average effluent concentrations of total inorganic nitrogen (TIN) and PO43--P during the stable operation period were 1.8 and 0.3 mg/L, respectively. PN was achieved with an average nitrite accumulation ratio of 90.4 % by combined strategies. Adequate storage of polyhydroxyalkanoates and glycogen in the anaerobic zone promoted the subsequent nitrogen removal capacity. In the anoxic zone, nitrite served as the main electron acceptor for the denitrifying phosphorus removal process. Mass balance analysis revealed that nDNPR contributed to 23.6 % of TIN removal and 44.7 % of PO43--P removal. The enrichment of Nitrosomonas (0.45 %) and Ellin 6067 (1.31 %), along with the washout of Nitrospira (0.15 %) provided the bacterial basis for the successful implementation of PN. Other dominant endogenous heterotrophic bacteria, such as Dechlormonas (10.81 %) and Candidatus Accumulibacter (2.96 %), ensured simultaneous nitrogen and phosphorus removal performance. The successful validation of integrating PN, ED and nDNPR for advanced nutrient removal in the AOA-SDR process provides a transformative technology for WWTPs.

The successful application of light to the system of simultaneous nitrification/endogenous denitrification and phosphorus removal: Promotion of partial nitrification and glycogen accumulation metabolism.

Partial nitrification (PN) and high glycogen accumulating metabolism (GAM) activity are the basis for efficient nitrogen (N) and phosphorus (P) removal in simultaneous nitrification endogenous denitrification and phosphorus removal (SNDPR) systems. However, achieving these processes in practical operations is challenging. This study proposes that light irradiation is a novel strategy to enhance the nutrient removal performance of the SNDPR system with low carbon to nitrogen ratios (C/N of 3.3-4.1) domestic wastewater. Light energy densities (Es) of 55-135 J/g VSS were found to promote the activity of ammonia-oxidizing bacteria (AOB) and GAM, while inhibiting the activity of nitrite-oxidizing bacteria (NOB) and polyphosphate accumulating metabolism (PAM). Long-term exposure to different light patterns at Es of 55-135 J/g VSS revealed that continuous light rapidly achieved PN by inhibiting NOB activity and promoted the growth of glycogen accumulating organisms (GAOs), allowing the removal of above 82 % N and below 80 % P. Intermittent light maintained stable PN by inhibiting the activity and growth of NOB and promoted the growth of polyphosphate accumulating organisms (PAOs) with high GAM activity (Accmulibacer IIC-ii and IIC-iii), allowing the removal of above 82 % N and 95 % P. Flow cytometry and enzyme activity assays showed that light promoted GAM-related enzyme activity and the metabolic activity of partial Accmulibacer II over other endogenous denitrifying bacteria, while inhibiting NOB translation activity. These findings provide a new approach for enhancing nutrient removal, especially for achieving PN and promoting GAM activity, in SNDPR systems treating low C/N ratio domestic wastewater using light irradiation.

Simultaneous partial nitrification, denitrification, and phosphorus removal in sequencing batch reactors via controlled reduced aeration and short-term sludge retention time decrease.

Simultaneous bio-treatment processes of organic carbon (C)-, nitrogen (N)-, and phosphorus (P)-containing wastewater are challenged by insufficient carbon sources in the effluent. In the present study, two parallel anaerobic/aerobic sequencing batch reactors (R-1 and R-2) treating low C/N (≤4) wastewater were employed using different partial nitrification start-up strategies, controlled reduced aeration, and decreased sludge retention time. Advanced removal efficiencies for NH4+-N (≥96%), total nitrogen (TN, ≥86%), PO43--P (≥95%), and CODintra (≥91%) were realized, with TN and PO43--P effluent concentrations of 10.0 ± 3.5 and 0.11 ± 0.3 mg/L in R-1 and 9.28 ± 4.0 and 0.11 ± 0.1 mg/L in R-2, respectively. Higher nitrite accumulation rate (nearly 100%) and TN (121.1 ± 0.7 mg TN/g VSS·d) and P (12.5 ± 0.6 mg PO43--P/g VSS·d) removal loadings were obtained in R-2 by a thorough elimination of nitrite-oxidizing bacteria. Moreover, different microbial structures and nutrient removal pathways were identified. Denitrifying glycogen-accumulating organisms (Candidatus Competibacter) and phosphorus-accumulating organisms (PAOs) (Tetrasphaera) removed N and P with partial nitrification-endogenous denitrification pathways and aerobic P removal in R-1. In R-2, aerobic denitrifying bacteria (Psychrobacter) and PAOs ensured N and P removal through the partial nitrification-aerobic denitrification and aerobic P removal pathways. Compared to R-1, R-2 offers greater efficiency, convenience, and scope to further reduce carbon-source demand.

Insights on biological phosphorus removal with partial nitrification in single sludge system via sidestream free ammonia and free nitrous acid dosing.

The sidestream sludge treatment by free ammonium (FA)/free nitrous acid (FNA) dosing was frequently demonstrated to maintain the nitrite pathway for the partial nitrification (PN) process. Nevertheless, the inhibitory effect of FA and FNA would severely influence polyphosphate accumulating organisms (PAOs), destroying the microbe-based phosphorus (P) removal. Therefore, a strategic evaluation was proposed to successfully achieve biological P removal with a partial nitrification process in a single sludge system by sidestream FA and FNA dosing. Through the long-term operation of 500 days, excellent phosphorus, ammonium and total nitrogen removal performance were achieved at 97.5 ± 2.6 %, 99.1 ± 1.0 % and 75.5 ± 0.4 %, respectively. Stable partial nitrification with a nitrite accumulation ratio (NAR) of 94.1 ± 3.4 was attained. The batch tests also reported the robust aerobic phosphorus uptake based on FA and FNA adapted sludge after exposure of FA and FNA, respectively, suggesting the FA and FNA treatment strategy could potentially offer the opportunity for the selection of PAOs, which synchronously have the tolerance to FA and FNA. Microbial community analysis suggested that Accumulibacter, Tetrasphaera, and Comamonadaceae collectively contributed to the phosphorus removal in this system. Summarily, the proposed work presents a novel and feasible strategy to integrate enhanced biological phosphorus removal (EBPR) and short-cut nitrogen cycling and bring the combined mainstream phosphorus removal and partial nitrification process closer to practical application.

Achieving advanced nitrogen removal from low-carbon municipal wastewater using partial-nitrification/anammox and endogenous partial-denitrification/anammox.

To achieve advanced nitrogen removal from low-carbon wastewater, a partial-nitrification/anammox and endogenous partial-denitrification/ anammox (PN/A-EPD/A) process was developed in a sequential batch biofilm reactor (SBBR). Advanced nitrogen was achieved with the effluent total nitrogen (TN) of 3.29 mg/L when the influent COD/TN and the TN were 2.86 and 59.59 mg/L, respectively. This was attributed to a stable PN/A-EPD/A, which was achieved through the integration of four strategies, including treating the inoculated sludge with free nitrous acid, inoculating anammox biofilm, discharging excess activated sludge and residual ammonium at the end of oxic stage. The 16S rRNA high-throughput sequencing results demonstrated that anammox bacteria coexisted with ammonia oxidizing bacteria, nitrite oxidizing bacteria, denitrifying glycogen accumulating organisms (DGAOs) and denitrifying phosphorus accumulating organisms (DPAOs) in biofilms. The abundance of anammox bacteria in the inner layer of the biofilm is higher, while that of DGAOs and DPAOs is higher in the outer layer.

A novel process for anammox pretreatment of municipal wastewater: semi-partial nitrification, biological phosphorus removal and recovery.

Achieving simultaneous semi-partial nitrification and deep phosphorus removal is a preferred process technology for Anammox pretreatment. In this study, semi-partial nitrification combined with in-situ phosphorus recovery (PNPR) was used to treat municipal wastewater. The SRT conflict between the nitrification and phosphorus removal was resolved by in-situ phosphorus recovery every 20 cycles of Anaerobic/Oxid, and a supernatant with more than 10 times the influent phosphorus concentration was obtained, thus achieving bio-enhanced phosphorus removal and recovery with satisfactory semi-partial-nitrification effluent. Interestingly, the results showed that phosphorus removal and recovery process could improve the activity of AOB. The PNPR system's nitrite accumulation rate (NAR) and phosphorus removal rate (PRR) were more than 90% each, whereas the relative abundance of AOB and PAOs increased from 0.04% to 0.74% and from 0.25% to 0.70%, respectively (P < 0.01). Furthermore, on average, the NO2--Neff/NH4+-Neff value was 1.96, which laid the foundation for the subsequent anammox treatment.

Partial Nitrification and Enhanced Biological Phosphorus Removal in a Sequencing Batch Reactor Treating High-Strength Wastewater.

Complex and high levels of various pollutants in high-strength wastewaters hinder efficient and stable biological nutrient removal. In this study, the changes in pollutant removal performance and microbial community structure in a laboratory-scale anaerobic/aerobic sequencing batch reactor (SBR) treating simulated pre-fermented high-strength wastewater were investigated under different influent loading conditions. The results showed that when the influent chemical oxygen demand (COD), total nitrogen (TN), and orthophosphate (PO43--P) concentrations in the SBR increased to 983, 56, and 20 mg/L, respectively, the COD removal efficiency was maintained above 85%, the TN removal efficiency was 64.5%, and the PO43--P removal efficiency increased from 78.3% to 97.5%. Partial nitrification with simultaneous accumulation of ammonia (NH4+-N) and nitrite (NO2--N) was observed, which may be related to the effect of high influent load on ammonia- and nitrite-oxidising bacteria. The biological phosphorus removal activity was higher when propionate was used as the carbon source instead of acetate. The relative abundance of glycogen accumulating organisms (GAOs) increased significantly with the increase in organic load, while Tetrasphaera was the consistently dominant polyphosphate accumulating organism (PAO) in the reactor. Under high organic loading conditions, there was no significant PAO-GAO competition in the reactor, thus the phosphorus removal performance was not affected.

Enhanced simultaneous partial nitrification and denitrification performance of aerobic granular sludge via tapered aeration in sequencing batch reactor for treating low strength and low COD/TN ratio municipal wastewater.

The aerobic granular sludge simultaneous partial nitrification, denitrification and phosphorus removal (AGS-SPNDPR) process was carried out via tapered aeration in sequencing batch reactor (SBR) for treating low strength and low COD/TN ratio municipal wastewater. The results showed that aerobic granular sludge was successfully cultivated with good sedimentation performance when treating the municipal wastewater. Meanwhile, the median granule size increased to 270 (R1) and 257 (R2) µm on day 80. The excellent removal performance of COD (92%) and NH4+-N (95%) were achieved under different aeration modes, while the higher TN removal efficiency (76%) was achieved by tapered aeration. The accumulation of NO2--N in R2 indicated that the tapered aeration was beneficial to achieve simultaneously partial nitrification and denitrification. Meanwhile, the high-efficiency phosphorus (95%) removal was realized via additional carbon source, and SPNDPR process was formed under tapered aeration. The bacterial community analysis indicated denitrifying glycogen-accumulating organisms (DGAOs) Candidatus_Competibacter and ammonia-oxidizing bacteria (AOB) Nitrosomonas were more effectively enriched via tapered aeration, while phosphorus-accumulating organisms (PAOs) Candidatus_Accumulibacter were effectively enriched under additional organic carbon. AOB, denitrifying bacteria and PAOs were simultaneously enriched by tapered aeration and additional carbon source, which was beneficial to nutrients removal. This study might be conducive to the application of AGS-SPNDPR system for treating low strength and low COD/TN ratio municipal wastewater under tapered aeration.

Achieving combined biological short-cut nitrogen and phosphorus removal in a one sludge system with side-stream sludge treatment.

Biological nitrogen (N) removal via the short-cut pathway (NH4+-N→NO2--N→N2) is economically attractive in wastewater treatment plants (WWTPs). However, biological phosphorus (P) removal processes remain a bottleneck in these systems due to the strong inhibitory effect of nitrite or its protonated form (HNO2, free nitrous acid - FNA) on polyphosphate accumulating organisms (PAOs). In this study, a novel combined nitrogen and phosphorus removal strategy was verified and achieved in a biological short-cut nitrogen removal system via side-stream sludge treatment with FNA, and the mechanisms impacting this process were investigated. The side-stream FNA treatment process applied here led to a significant reduction in the real sludge retention time (SRT) in the mainstream (approximately 2.7 days) based on the biocidal effect of FNA to the majority of the organisms. This work also found that around 40% of the P uptake activity was still maintained at a much higher FNA level of 38 µg N/L with potential PAOs, which highly broadened the current knowledge of PAOs community. An economic analysis revealed advantages of the proposed as compared to conventional biological nitrogen and phosphorus removal (13% savings in total cost), biological short-cut nitrogen removal (via FNA treatment) with chemical phosphorus precipitation (21% savings) and conventional biological nitrogen removal with chemical precipitation (27% savings). Overall, this study presents a novel and viable retrofit strategy in integrating biological short-cut nitrogen removal with EBPR for next generation WWTPs.

Rapidly achieving partial nitrification of municipal wastewater in enhanced biological phosphorus removal (EBPR) reactor: Effect of heterotrophs proliferation and microbial interactions.

Stable nitritation is the major challenge for short-cut nitrogen removal from municipal wastewater. This paper demonstrated a rapid achievement of partial nitrification (PN) in an enhanced biological phosphorus removal (EBPR) reactor treating domestic wastewater. Polyphosphate accumulating organisms (PAOs) were enriched operated at a short aerobic HRT (2.0 h) and SRT (10 d), with satisfactory phosphorus removal efficiency (95.9%). Both of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) were elutriated simultaneously. Interestingly, AOB recovered much faster than NOB by a subsequent extension of aerobic HRT and SRT, resulting in a rapid development of PN within 15 days. Ammonia oxidation rates of AOB significantly increased by 44.2%, facilitating a high nitrite accumulation rate (NAR) of 95.8%. Genus Tetrasphaera, Halomonas, Paracoccus and Candidatus_Accumulibacter belonging to PAOs accounted for 4.6%. The proliferation of heterotrophs, typically as PAOs, maximized the microbial competition against NOB by favoring AOB activity and synergy with functional bacteria.

Enhanced nutrient removal and facilitating granulation via intermittent aeration in simultaneous partial nitrification endogenous denitrification and phosphorus removal (SPNEDpr) process.

A novel simultaneous partial nitrification, endogenous denitrification and phosphorus removal (SPNEDpr) system was operated for 213 days in a sequencing batch reactor to treat real domestic sewage. The nutrient removal was achieved under an operation mode of intermittent aeration at unequal intervals with low oxygen concentrations. Through optimizing intermittent aeration conditions, the removal efficiencies of total inorganic nitrogen (TIN), PO43-P and chemical oxygen demand (COD) reached 78.40%, 98.13% and 84%, respectively. Low-oxygen (0.1-0.7 mg/L) and intermittent aeration effectively inhibited nitrite oxidation bacteria (NOB), maintaining stable partial nitrification with nitrite accumulation ratio of 96.45%. Notably, intermittent aeration promoted the formation of aerobic granular sludge, with the sludge particle size increasing from 217.2 ± 5.3 to 351.8 ± 4.8 µm, thereby enhancing the TIN loss efficiency (81.3%). The predominant genus was Candidatus_Competibacter (11.6%), which stored COD as intracellular carbon source and performed the endogenous denitrification. The SPNEDpr process provided a highly efficient and economical method for treating urban sewage.

A novel denitrifying phosphorus removal and partial nitrification, anammox (DPR-PNA) process for advanced nutrients removal from high-strength wastewater.

This study developed a novel DPR-PNA (denitrifying phosphorus removal, partial nitrification and anammox) process for sustaining high-strength wastewater treatment in a modified continuous flow reactor without external carbon source. After 259-days operation, a synchronous highly-efficient total inorganic nitrogen, PO43--P and CODcr removal efficiencies of 88.5%, 89.5% and 90.1% were obtained, respectively even influent nitrogen loading rate up to 3.2 kg m-3 d-1. Batch tests revealed that denitrifying phosphorus accumulating organisms (DPAOs) using NO3--N as electron acceptors significantly enriched (74% in total PAOs), which emerged remarkable positive impacts on deep-level nutrient removal as the key limiting factor. Furthermore, the NO2--N inhibitory threshold value (∼20.0 mg L-1) for DPAOs was identified, which demonstrated as an inhibitory component in excessive recycling NOx--N. From the molecular biology perspective, Dechloromonas-DPAOs group (18.59%) dominated the excellent dephosphatation performance, while Nitrosomonas-AOB (ammonia oxidizing bacteria) group (16.26%) and Candidatus_Brocadia-AnAOB (anammox bacteria) group (15.12%) were responsible for the desirable nitrogen loss process. Overall, the present work highlighted the novel DPR-PNA process for nutrients removal is a promising alternation for wastewater of high nitrogen but low carbon.

Facilitating sludge granulation and favoring glycogen accumulating organisms by increased salinity in an anaerobic/micro-aerobic simultaneous partial nitrification, denitrification and phosphorus removal (SPNDPR) process.

This study used salinity (0.5 wt%, 0.75 wt%) to accelerate the formation of ammonia oxidizing bacteria (AOB)-enriched aerobic granular sludge in a lab-scale anaerobic/micro-aerobic simultaneous partial nitrification, denitrification and phosphorus removal (SPNDPR) reactor. Results confirmed that the average granule diameter increased from 298.7 to 425.4 µm after 45 days of salinity stress even with low dissolved oxygen. Extracellular polymeric substances increased from 149.5 to 387.7 mg/g VSS after salinity (0.75 wt%) treatment, in turn accelerating granulation. Partial nitrification was maintained under the salinity condition due to the relative high activity and abundance of AOB, and the observed nitrite accumulation ratio averaged 98.9%. Salinity favored glycogen-accumulating organisms over polyphosphate-accumulating organisms (PAOs)/denitrifying-PAOs, with the abundance of Candidatus_Competibacter increasing from 4.86% to 15.34% and the simultaneous partial nitrification-denitrification efficiency increasing from 74.4% to 91.1%, promoting N-removal potential. The P-removal performance was good under 0.5 wt% salinity but was inhibited under 0.75 wt% salinity.

Enhanced nutrient removal of simultaneous partial nitrification, denitrification and phosphorus removal (SPNDPR) in a single-stage anaerobic/micro-aerobic sequencing batch reactor for treating real sewage with low carbon/nitrogen.

The feasibility of simultaneous partial nitrification, denitrification and phosphorus removal (SPNDPR) process was investigated in a single-stage anaerobic/micro-aerobic sequencing batch reactor for treating real sewage. Partial nitrification was maintained with average nitrite accumulation ratio of 90.3% during 266 days' operation. Removal efficiencies for NH4+-N (96.3%), total inorganic nitrogen (81.4%), and phosphorus (91.0%) were stably obtained when treated real sewage with low carbon/nitrogen (3.4), with simultaneous partial nitrification and denitrification efficiency of 73.1%. The mechanism analysis revealed that denitrifying glycogen-accumulating organisms (DGAOs) and denitrifying polyphosphate-accumulating organisms (DPAOs) played the main roles in N-removal and P-removal, respectively. Nitrite pathway and optimized use of the organic carbon available in the sewage were keys for the successful performance. Further microbial community illustrating that DGAOs Candidatus_Competibacter, DPAOs Dechloromonas, and ammonia-oxidizing bacteria Nitrosomonadaceae were main functional groups. Notably, sludge granulation was formed under long-term synchronous low dissolved oxygen and low sludge loading conditions, avoiding sludge bulking.

Achieving deep-level nutrient removal via combined denitrifying phosphorus removal and simultaneous partial nitrification-endogenous denitrification process in a single-sludge sequencing batch reactor.

The feasibility of coupling denitrifying phosphorus removal (DPR) with simultaneous partial nitrification-endogenous denitrification (SPNED) was investigated in a single-sludge sequencing batch reactor for deep-level nutrient removal from municipal and nitrate wastewaters. After 160-day operation, the DPR process simultaneously reduced most PO43--P and NO3--N anoxically, and the SPNED process achieved further total nitrogen (TN) removal at low dissolved oxygen condition with TN removal efficiency of 90.8%. The effluent NH4+-N, PO43--P and TN concentrations were 1.0, 0.1 and 7.2 mg/L, respectively. Microbial analysis revealed that Dechloromonas (6.7%) dominated DPR process, whereas the gradually enriched Nitrosomonas (4.5%) and Candidatus Competibacter (6.8%) conducted SPNED process accompanied with sharply eliminated Nitrospirae (1.4%). Based on these findings, a novel strategy was proposed to achieve further nutrient removal in conventional treatment through integrating the DPR-SPNED process. As a result, ∼100% of extra carbon and ∼10% of oxygen consumptions would be reduced with satisfactory effluent quality.

Improvement of partial nitrification endogenous denitrification and phosphorus removal system: Balancing competition between phosphorus and glycogen accumulating organisms to enhance nitrogen removal without initiating phosphorus removal deterioration.

The novel partial nitrification endogenous denitrification and phosphorus removal (PNEDPR) process can achieve deep-level nutrient removal from low carbon/nitrogen municipal wastewater without extra carbons. However, its performance is limited by long hydraulic retention time (HRT) and low specific endogenous denitrification rate (rNO2). This study aimed at investigating the effects of two improving strategies on PNEDPR. One was decreasing both anaerobic and anoxic reaction time for shortening HRT from 55 h to 17.5 h. The other was temporarily discharging orthophosphate-rich supernatant for balancing the competition between phosphorus and glycogen accumulating organisms to further raise rNO2 without deterioration of phosphorus removal. Results revealed that, desirable nutrient removal was obtained, as average effluent concentrations of total nitrogen and orthophosphate were 8.4 and 0.5 mg/L with their average removal efficiencies of 86.8% and 90.9%. High-throughput sequencing analysis revealed that, Candidatus_Competibacter conducted nitrogen removal endogenous denitrification and Candidatus_Accumulibacter and Tetrasphaera ensured phosphorus removal.

[Denitrification and Phosphorus Removal from Low C/N Urban Sewage Based on a Post-Partial Denitrification AOA-SBR Process].

This study focuses on the investigation of the nitrogen (N) and phosphorus (P) removal characteristics of a combination of enhanced phosphorus removal (EBPR) with simultaneous partial nitrification endogenous denitrification (SPND) and post-partial denitrification process. An anaerobic/aerobic/anoxic (A/O/A) operated sequencing batch reactor (SBR) fed with urban sewage was optimized by regulating the aeration rate and anoxic time. Based on this optimization, deep-level nitrogen and phosphorus removals from low C/N urban sewage could be realized. The experimental results show that the effluent PO43--P concentration decreased from 0.06 mg·L-1 to 0 mg·L-1, the effluent NH4+-N, NO2--N, and NO3--N concentrations gradually decreased from 0.18, 18.79, and 0.08 mg·L-1 to 0, 16.46, and 0.05 mg·L-1, respectively, and the TN removal efficiency increased from 72.69% to 77.97% when the aeration rate decreased from 1.0 L·min-1 to 0.6 L·min-1 and the anoxic duration was 180 min. With the reduction of the aeration rate, the SPND phenomenon became notable and the SND rate increased from 19.18% to 31.20%. When the anoxic duration was extended from 180 min to 420 min, the effluent PO43--P, NH4+-N, and NO3--N concentrations stabilized at~0, 0, and 0.03 mg·L-1, respectively. The effluent NO2--N concentration was as low as 3.06 mg·L-1, the SND rate was~32.21%, the TN removal performance gradually improved, and the TN removal efficiency was as high as 99.42%. Thus, deep-level nitrogen and phosphorus removals could be realized with the SPNDPR-PD system.

Combining partial nitrification and post endogenous denitrification in an EBPR system for deep-level nutrient removal from low carbon/nitrogen (C/N) domestic wastewater.

In this study, partial nitrification and post endogenous denitrification (PED) were combined with enhancing bacterial phosphorus removal (EBPR) in an anaerobic/aerobic/anoxic operated sequencing batch reactor (SBR) for deep-level nutrient removal from low carbon/nitrogen (C/N, chemical oxygen demand (COD)/total nitrogen (TN)) domestic wastewater. At anaerobic stage, abundant organic matters (96.6% of COD consumption) in raw wastewater were stored as poly-hydroxyalkanoates (PHAs) by phosphorus and glycogen accumulating organisms with enhanced activities, which provided sufficient intracellular carbons for subsequent aerobic phosphorus uptake and anoxic PED. By controlling suitable aeration rate and duration, high nitrite accumulation rate (97.2%) was obtained at aerobic stage, which saved intracellular carbons consumption of PED. Moreover, the subsequent utilization of glycogen after PHAs via PED ensured the deep-level TN removal (94.9%) without external carbon addition. After 160-day operation, the average effluent PO43--P and TN concentrations were 0.4 and 3.0 mg/L, respectively, at C/N of 3.1.

[Effect of Aerobic/Phosphorus Granules on Start-up of Partial Nitrification Granular Sludge].

The different effects of additional aerobic granules (AGs) and phosphorus removal granules (PRGs) on the start-up and stable operation of partial nitrification granular sludge (PNGS) were compared at room temperature(22-28℃). The results showed that in the first stage (days 0-22), partial nitrification was accomplished on day 19 for the three reactors (R1, R2, and R3). In the second stage (days 23-56), 20% AGs and 20% PRGs were added to R2 and R3 to induce PNGS. The start-up of the granules of the three reactors was successfully achieved. The mean particle sizes of R1, R2, and R3 reached 412 µm at day 76, 468 µm at day 42, and 400 µm at day 56. In the third stage (days 57-108), because the influent ammonia load increased from 0.4 kg·(m3·d)-1 to 0.5 kg·(m3·d)-1 and the COD load increased from 0.2 kg·(m3·d)-1 to 0.5 kg·(m3·d)-1, the mean particle sizes of R1 and R2 increased significantly. The average particle sizes of R1 and R2 reached 689 µm and 893 µm by the end of the operation (day 108), but sludge expansion occurred in R3. The inoculation of either AGs or PRGs could quickly achieve granulation, but the PNGS inoculated with the AGs could adapt to higher C/N and be more tolerable to shock loads and long-term stable operation.

Textile dye biodecolourization and ammonium removal over nitrite in aerobic granular sludge sequencing batch reactors.

Biodecolourization of azo dye and removal of ammonium by aerobic granular sludge (AGS) was investigated under different growth conditions. AGS not previously exposed to azo dye was able to effectively decolourize azo dye under anaerobic and microaerophilic conditions. Azo dye, total organic carbon and ammoniacal nitrogen removal efficiencies of 89-100%, 79-95% and 92-100%, respectively, were achieved in the AGS reactor operated for 80days under microaerophilic conditions. Removal of carbon, nitrogen and phosphorus was not impacted by azo dye loading. Azo dye, organic carbon and ammonium were majorly removed in the anoxic period wherein bulk dissolved oxygen was ranged from 0.5 and <0.08mgL-1. Removal of 60mgL-1 NH4+-N was associated only with smaller amounts of nitrite build-up (∼5mgL-1 NO2--N) and negligible nitrate concentrations. Profiles of nitrogen compounds in individual sequencing batch reactor cycles supported the occurrence of ammonium removal over nitrite pathway. Bacterial community analysis showed enrichment of specific microorganisms capable of decolourizing azo dyes in the dye-decolourizing AGS. Dye decolourization and nutrient removal by AGS under microaerophilic conditions is a novel finding and can be further developed for treating textile wastewaters onsite or after dilution with sewage.